Exit status

Check this post to learn about exit status :

https://jrichardsz.github.io/linux/exit-status-of-a-command

sdout stderr

This is well known as standard output. Do you remember this in c++ ? :

cout >> "Hello worl c++";

Or in java :

System.out.println("Hello world java");

So if you create some awesome tool and use this sentences, when a client uses it, his console will show your “Hello world …”

Thank you so much for existing

When you develop some devops scripts , stdout is almost a pain in my &%&%%$#$%# because screen console is contaminated with uncontrolled messages.

But some times, stdout helps for example with sqlplus tool.

sqplus does not return a nonzero value for errors. So the only way to detect if a command was successful is to interpret stdout message.

For example:

sqlplus user/password@sid < sqlfile.sql

In case of some error , return :

ERROR at line 1:
ORA-01403: no data found
ORA-06512: at "TAROT.TEST_PROC", line 4
ORA-06512: at line 1

But $? exit status is zero, so we can’t use exit status to detect success or failure for this tool.

Parsing stdout message

Given the last case, this script could help you to detect success or error :

Get message as var:

sqlplus_message=$(sqlplus user/password@sid < sqlfile.sql)

Check for ERROR string in sqlplus_message

if [[ $sqlplus_message == *"ERROR"* ]]; then
  echo "success"
else
  echo "success"
fi

Disable stdout and stderr

In many cases, stdout must be disabled to ensure a clean console messages.

For example, this script:

mvn_detect() {
  maven_version=$(mvn -v)
  status=$?
  echo $status
}

echo "status:$(mvn_detect)"

return :

mvm.sh: line 2: mvn: command not found
status:127

This line is not required : mvm.sh: line 2: mvn: command not found. I don’t review linux code but I think that this is a kind of stdout, so for disabled it I used:

> /dev/null 2>&1

mvn_detect() {
  maven_version=$(mvn -v > /dev/null 2>&1)
  status=$?
  echo $status
}
echo "status:$(mvn_detect)"

and the result was clean:

status:127

That’s it for today.

Until the next,
JRichardsz